(a) Field of the Invention
The present invention relates to a transmission line, and more particularly to a transmission line with better characteristic impedance (Z0) and high flexibility.
(b) Description of the Related Art
With reference to FIG. 1 for transm+itting a LVDS signal, the signal communication between a liquid crystal display (LCD) and a host system involves a huge volume and a very high frequency, and thus the high frequency signal transmission established between an LCD interface 6 and a system motherboard interface 7 adopts a low voltage differential signal (LVDS) transceiver 9 with a super high speed (1.4 Gb/s), a low power consumption and a low electromagnetic interference (EMI) as the signal transmission interface of the LCD interface 6, and a signal transmission line 9 is provided for connecting the signal transmission interface of the system motherboard interface 7 (which is a connector socket 71 of the system motherboard interface 7) for a conventional LVDS signal transmission.
According to a LVDS interface standard defined by ANSI-YUA-EIA-644-I995, a signal transmission line 9 for a LVDS signal transmission must be a signal transmission line 9 with a characteristic impedance (Z0) equal to 100Ω±5% before the impedance (Z) of a circuit between the LCD interface 6 and the system motherboard interface 7 can be matched, and the LVDS signal transmission must satisfy this condition to achieve the effects of reducing the electromagnetic inference and noises, correctly executing the signal transmission between the LCD interface (or LVDS interface) 6 and the system motherboard interface 7 and preventing errors. If the aforementioned condition is not satisfied, signal reflections, noises, data loses, deformations or distortions may occur in signal transmissions between the LCD interface 6 and the system motherboard interface 7.
With reference to FIG. 2A for a schematic view of a conventional signal transmission line, a thicker insulating layer 92 and a metal layer 93 are attached sequentially on a surface of a flexible flat cable 91. With reference to FIG. 2B, the thickness of a plastic film layer 911 of a flexible flat cable 91 is increased to improve the insulating thickness of the flexible flat cable 91 for producing a compliant characteristic impedance (Z0). Regardless of increasing the thickness of the plastic film layer 911 or adding the insulating layer 92, a specific thickness of a poly (ethylene terephthalate (PET) material is required for complying with the requirements of the characteristic impedance (Z0), and its hardness will be relatively higher, and thus the flexible flat cable 91 complies with the required characteristic impedance (Z0) but the flexibility becomes lower, and the operation of the whole signal transmission line 9 becomes less flexible.